Synthesis And Electrochemical Properties Of Silicon/Titanium Niobium Oxide Composites As Anode Materials For Lithium-ion Batteries

In recent years,the rapid development of artificial intelligence equipment and new mobile devices has made higher demands on lithium-ion battery technology.As an essential part of lithium-ion batteries,anode material largely determines their capacity and cycling performance.Silicon,a new type of anode material,attracts more and more attention owing to its high specific capacity,low prices,and the environmentally friendly feature.However,the serious volume effect and poor conductivity of silicon severely limit its practical application and future development.This thesis makes the first attempt on the preparation of silicon/titanium niobium oxide composites which use silicon as reinforcement and niobium titanium oxide as matrix.By constructing stress buffer layer and ion exchange layer around the silicon particles,the composites contributes to buffering volume effect and improving electrical contact.The composites are mainly prepared with ball milling method and high-temperature solid phase method.This thesis researches on the optimal parameters of the preparating process and studies the electrochemical performance.Considering the results,the thesis also raises an optimization directing at the high temperature solid phase method.Ball milling method takes duration,mixing speed,and the proportion of silicon incorporation into consideration.The optimal preparation program is:first,with 60%wt%Si incorporation,at the speed of 200r/min,doing wet milling mixing for 5h to get the reaction precursor;second,drying the reaction precursor f'or 8h and then solid milling at the speed of 450r/min for 30h to get the composites.The composite anode material prepared with this method possesses first charge-discharge specific capacity of 1367mAh/g;the figure remains 85mAh/g after 50 cycles.High-temperature solid phase method studies temperature,duration,and the proportion of silicon incorporation,and makes sure the optimal preparation program:under the condition of 60wt%Si incorporation and 1000?,insulating for 2h with heat treatment.The silicon/titanium niobium oxide composites prepared with this method possesses first charge-discharge specific capacity of 1447.8mAh/g,the figure remains 220mAh/g after 50 cycles.By contrasting the two methods,the composites prepared with high temperature solid phase method present better cycling performance.Based on the program of high temperature solid phase method,the thesis makes a futher optimization:to replace the initial magnetic stirring mixing with wet milling mixing;to replace the initial PVDF binder with CMV binder.The anode material prepared by the optimized program has first charge-discharge specific capacity of 1258mAh/g,and the figure remains 390mAh/g after 50 cycles.This figure surpasses the currently commercially applied graphite anode materials(372mAh/g)by 10%in terms of specific capacity.The thesis believes that to study the silicon/titanium niobium oxide composites which use silicon as reinforcement and niobium titanium oxide as matrix is not only significant but also promising.